1. Field of the Invention
This invention relates to a fault management system for managing faults in the terminating circuits of a telecommunications network and also to a method of operating such a fault management system.
2. Related Art
A conventional public telecommunications network comprises a relatively small number of interconnected main switches and a much larger number of local switches, each of which is connected to one or two main switches. The local switches are connected to the terminating circuits of the network and the far ends of these circuits are connected to terminal equipment such as telephone instruments provided for users of the network. The network formed from the main switches and local switches is known as the core network while a network formed from the terminating circuits is known variously as an access network or a local loop. In this specification, it will be referred to as an access network. Some terminating circuits are connected to a remote concentrator, which may or may not have switching capability. The remote concentrator is then connected to a local switch. In this specification, the term "local switch" is to be interpreted to cover both local switches and remote concentrators.
In a conventional access network, each terminating circuit is formed from a pair of copper wires. Typically, each pair of copper wires pass through a series of nodes between the local switch and terminal equipment. Examples of such nodes are primary cross-connect points, secondary cross-connect points, distribution points and joints.
Recently, optical fibres have been used to carry terminating circuits in access networks. In a modern access network, both pairs of copper wires and optical fibres are used to carry the terminating circuits. Where a terminating circuit is carried by an optical fibre, the circuit will typically pass through several nodes between the local switch and the terminal equipment. At each node, the incoming fibre from the local switch is split into a group of outgoing fibres which branch out in various directions. Where a terminating circuit is carried by an optical fibre from the local switch, the last part of the circuit may be carried by a pair of copper wires.
Unfortunately, terminating circuits are prone to faults. In a conventional access network, examples of such faults are disconnection, a short circuit between the two wires of a pair of wires, and a short circuit between one of the wires and earth. The causes of the faults include ingress of water into a node and also physical damage to a node.
Local switches are provided with circuit testing apparatus which may be used to test its terminating circuits. When a customer reports a fault on a terminating circuit, the circuit may then be tested to identify the fault condition. In order to repair the fault, it is present practice for an engineer to make a guess at the location of the fault and open the node at that location. If the engineer's guess is wrong, he will have to open one or more further nodes before finding and repairing the fault. Sometimes an engineer will have to open each node in turn between the local switch and the terminal equipment until he finds a node where the fault is present. Typically, in a conventional access network, an engineer will open between 2.5 and 3 nodes on average before locating a fault.
The present practice for locating faults thus suffers from two problems. Firstly, it is time consuming for an engineer to have to open several nodes before locating and repairing a fault. Secondly, as the nodes are of a delicate construction, each time an engineer opens a node he will damage the node with the result that there is another fault on a terminating circuit.